To a stirred solution of (2,2-dimethoxy-ethyl)-[1-(4-hydroxy-3-methoxy-phenyl-2-(3-methoxy-phenyl)-ethyl-carbamic acid ethyl ester (3.7 g, 8.55 mmol) in acetone (150 mL) was added 6N hydrochloric acid (38 mL) at 0° C. The reaction mixture was stirred at room temperature for 15 hrs. The mixture was diluted with water. The solvent was evaporated and the aqueous layer was extracted with ethyl acetate (3×100 mL). The combined extracts were washed with saturated aqueous sodium chloride solution (80 mL), dried over anhydrous magnesium sulfate, filtered and concentrated in vacuo. Flash chromatography (Merck Silica gel 60, 70–230 mesh, 50% ethyl acetate/hexane) afforded 6-hydroxy-7-methoxy-1-(3-methoxy-benzyl)-1H-isoquinoline-2-carboxylic acid ethyl ester (1.17, 37% yield) as a colorless oil.
